A guide vane for a gas turbine with a vane base body which is of single-piece design and comprises a profiled vane blade extending between a vane root and a cover plate and also the vane root formed integrally with the vane blade and the cover plate formed integrally with the vane blade, is intended, in a relatively simple way to be able to be matched to the individual conditions of use with especially little outlay on apparatus and logistics. For this purpose, according to the invention, a flow-routing body with an advance guide blade that is connected upstream of the vane blade as seen in the direction of flow of the working medium of the gas turbine is joined to the vane base body.